Physics 2B Lab Series R-C Circuit Time Constant Objective: To determine the time constant of an RC circuit Theory: A capacitor, C, creates an open or disconnected circuit. If the series circuit with a capacitor and resistor, R, is powered by direct current (DC) power supply or battery, charges will accumulate on the capacitor plates until the two have equal voltages. If the switch is closed at t=0, we find that the charge, q(t), on the capacitor at a later time, t, increases as follows q(t) =Q0 (1-e-t/RC ) 1. where e is equal to 2.718 The product RC is called the time constant, τ ., and represents the time it takes to increase the charge on the capacitor from zero to 63.2%. If the battery is removed from the circuit and the circuit reconnected the capacitor would also lose 63.2% of its charge in time t, or would decrease to down to 36.8% of Q0 . [ Refer to section 18.5 , on page 475, in course textbook] Materials Needed: 1. One 10 k Ω Resistor 2. One .01 υ F Capacitor 3. One Oscilloscope

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